External-to-internal numbering plan aliasing

ABSTRACT

External invocation of features on a switching system (10) from a network (18) is made possible by aliasing otherwise-unused network numbers that are assigned to the switching system within the network numbering plan to feature-access codes of the switching system&#39;s internal numbering plan, in the switching system&#39;s call processing arrangement (200) that uses stored definitions of syntax (320, 350) and grammar (400, 410) of the internal and network numbering plans. The aliasing is accomplished as follows. The syntax definitions of the internal numbering plan include definitions (312) of individual feature access codes, while the syntax definitions of the network numbering plan include definitions (312) of the aliased network numbers, which either are the same as the definitions of the corresponding feature access codes or direct the aliased network numbers to be translated into the corresponding feature access codes. In use, symbol strings received by the switching systems are parsed (210) to identify them as feature access codes or aliased network numbers, requisite translations are performed (230), and feature modules (205) that are pointed to (334) within the definitions are invoked (220).

CROSS-REFERENCE TO RELATED APPLICATIONS

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Telecommunications Call-Processing Arrangement";

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Dynamic Tone-Administration";

F. J. Bogart, B. D. Butterfield, D. L, Chavez, Jr., F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L Thomson, "Dynamic Routing-Administration";

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Dialed Number Recognition Arrangement";

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson "Use-Code Based Call-Treatment Selection"; and

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Context-Dependent Call-Feature Selection":

these applications were filed on Oct. 31, 1991, and are assigned the same assignee as this application.

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Arrangement for Effecting Segmentation of a Displayed Called Number";

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Mnemonic and Synonymic Addressing in a Telecommunications System"; and

F. J. Bogart, B. D. Butterfield, D. L. Chavez, Jr., H. C. Dittmer, F. R. Fix, L. J. Hardouin, N. K. Schmidt, and L. L. Thomson, "Shared-Tenant Services Arrangement Providing Numbering-Plan Independence and Cross-Plan Access to Tenant Groups":

these applications are being filed concurrently with this application and are assigned to the same assignee.

TECHNICAL FIELD

This invention relates generally to telephone and telephone-like communications systems including integrated services systems, and relates particularly to telephony call-processing arrangements.

BACKGROUND OF THE INVENTION

The internal numbering plan of a telecommunications switching system is the set of numbers (e.g., extensions, feature access codes) directly served by the switching system itself. It may be a subset of a network numbering plan of a telecommunications network of which the switching system is a part, or it may be a separate numbering plan from the network numbering plan.

Users who are directly served by the switching system (i.e., whose terminals are directly connected to the switching system) have direct access to the internal numbering plan; they can validly dial both the extension numbers and the feature access codes of the internal numbering plan. In contrast, switching systems typically provide only restricted external access to their internal numbering plans. That is, users who are not directly served by the switching system (i.e., whose terminals are connected to the switching system through other switching systems and through inter-system trunks in a telecommunications network) have direct access only to the extension numbers and have either no access or only indirect access to the feature access codes of the internal numbering plan.

Conventionally, external access to the internal numbering plan may be had in one of two ways. One way is to map the extension numbers of the internal numbering plan onto corresponding numbers of the network numbering plan. External users then dial network numbering plan numbers comprising the extension numbers prefixed by an office code that identifies the destination switching system to directly obtain call connections to corresponding internal extensions. But this scheme provides external access only to internal extension numbers and extensions and not to internal feature access codes and corresponding features. The other way is to have external users dial a single network numbering plan number to obtain a general call-connection to the destination switching system, obtain a second dial-tone from the accessed destination switching system in response as an indication that the switching system has been accessed, and thereafter dial the internal numbering plan extension numbers or feature access codes to obtain call connections to the corresponding extensions or feature modules just like internal users. But this scheme requires external users to first make themselves the equivalent of internal users, for purposes of accessing the internal numbering plan, by forcing them to first establish a connection to the switching system, and then to use this connection to input internal numbering plan numbers directly to the switching system as would internal users.

The reason for these restrictions on external access to the feature access codes of internal numbering plans is the failure of existing network numbering plans to provide for user selection of most features, and, in many cases, their failure to provide for the features at all. Consequently, these network numbering plans do not include user-invokable symbol sequences (e.g., user-dialable numbers) that correspond, within the network numbering plan itself, to the features or feature access codes of the internal numbering plans and which the users could invoke (dial) to access the features or feature access codes directly. In other words, the network numbering plans do not have feature access codes for internal numbering plan features.

A reason for entirely preventing external access to at least certain ones of the internal numbering plan feature access codes, such as long-distance network access codes, is to prevent abuses of the system, such as network toll fraud. But conventional switching system architectures make it very difficult, complex, and costly--if not impossible--to discriminate between different features and their access codes, so as to prevent external access to only certain features, or to limit external access thereto to authorized persons, yet permit external access to other, harmless, features such as leave-word calling. Consequently, designers of switching systems often "paint with a broad brush" and configure the systems to deny external access to all internal features and their access codes, even though optimally it is not desirable to do so.

Attempts have been made to overcome the limitations on external access to internal numbering plans. For example, U.S. Pat. No. 4,488,004 discloses an arrangement which allows direct external access to internal features of a private-branch exchange (PBX) in a PBX network, and thereby allows inter-PBX calls to appear to users as if they are served by a single large PBX. However, this arrangement requires the PBXs each to have an additional controller, and for these controllers to be interconnected by special dedicated control data links. This is a difficult, complex, and costly solution to the problem.

SUMMARY OF THE INVENTION

This invention is directed to solving these and other problems and disadvantages of the prior art. Generally according to the invention, a feature on a switching system is invoked from outside of the switching system by using a network numbering plan symbol-sequence (e.g., telephone number) that has been aliased in the switching system to stand for (e.g., has been defined to be an equivalent of) a feature access code of a feature within the switching system. Specifically according to the invention, a feature is invoked on a destination switching system having an internal numbering plan in a telecommunications network having a network numbering plan, in the following manner. To initiate the invocation, there is sent, from the network to the destination switching system, a network numbering plan symbol sequence which has been assigned within the network numbering plan to the destination switching system. According to a first aspect of the invention, the symbol sequence of the network numbering plan is assigned within the network numbering plan to a number that is otherwise reserved for an extension of the switching system. The origin of the sent symbol sequence is illustratively another, an originating, switching system in the network. The originating switching system may directly receive the network symbol sequence from a user, or it may generate it in response to some other input from the user that identifies a feature and the switching system on which that feature is to be invoked. The latter input may constitute, for example, an address (e.g., a telephone number) of the destination switching system accompanied by the originating switching system's feature access code for the desired feature. In any case, in response to receipt of the network numbering plan symbol sequence at the destination switching system, the received symbol sequence is interpreted at the destination switching system as a feature-invocation request. According to the first aspect of the invention, the received symbol sequence is interpreted to be an equivalent of a feature access code of a feature of the destination switching system, irrespective of whether that feature actually has or does not have a feature access code in the internal numbering plan of the destination switching system. According to a second aspect of the invention, the received symbol sequence is interpreted to be an equivalent of the feature's feature access code of the internal numbering plan of the destination switching system, even though the received symbol sequence and the feature access code are not one and the same symbol sequence, and do not even belong to the same numbering plan. In response to that interpretation, the like feature is invoked in the destination switching system as would be invoked by an internal numbering plan feature access code corresponding to that feature, for example, upon receipt of the feature access code from a user who is directly served by the destination switching system.

The invention characterized above provides the desired across-network feature-invocation facility without using any special inter-switching system control communication links. It provides external access to internal features, or feature access codes of the internal numbering plan, of a switching system via the network numbering plan more directly than does the prior art. Yet, at the same time, it provides the requisite system security, by providing external access only to those features whose feature access codes have been aliased to network numbers, thereby preventing external access to other features.

Further according to the invention, the features need not be invoked from outside of the switching system. Rather, a symbol sequence may be received from a user who is directly served by the switching system, and be treated in the same manner as described above. The symbol sequence may advantageously be an emergency-services access-number and result in invocation of an emergency-services feature within the switching systems itself, thereby illustratively ensuring that calls for emergency services from a plant (e.g., a building) served by the switching system will all be sent to the plant's internal emergency (e.g., security) service.

Also according to the invention, at least some of the switching system internal features that are externally invokable may not be internally invokable, i.e., they may not have corresponding feature access codes defined in the switching system's internal numbering plan, or use of their feature access codes may be denied to all or some internal users.

These and other advantages and features of the invention will become apparent from the following description of an illustrative embodiment of the invention considered together with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a telephone system that incorporates an illustrative embodiment of the invention;

FIG. 2 is a block diagram illustrating the convention of a network numbering plan of the telephone system of FIG. 1;

FIG. 3 is a block diagram of selected contents of the memory of the switching system of the telephone system of FIG. 1;

FIGS. 4-6 are block diagrams of syntax-defining data structures of network digit analysis of FIG. 3;

FIGS. 7-8 are block diagrams of grammar-defining data structures of network digit analysis of FIG. 3 showing data contents for a first illustrative network;

FIGS. 9-12 are a flow diagram of a string identification function of network digit analysis of FIG. 3;

FIG. 13 is a flow diagram of a string action function of network digit analysis of FIG. 3;

FIG. 14 is a block diagram of a data structure of digit modification of FIG. 3;

FIG. 15 is a flow diagram of a function of digit modification of FIG. 3;

FIGS. 16-18 are block diagrams of data structures of generalized route selection of FIG. 3;

FIG. 19 is a flow diagram of a function of generalized route selection of FIG. 3;

FIGS. 20-21 are block diagrams of data structures of digit sending of FIG. 3;

FIG. 22 is a flow diagram of a function of digit sending of FIG. 3; and

FIGS. 23-24 are block diagrams of grammar-defining data structures of network digit analysis of FIG. 3 showing data contents for a second illustrative network.

DETAILED DESCRIPTION

An illustrative embodiment of the invention is implemented in a telecommunications system shown in FIG. 1. The system of FIG. 1 is a telephone system that includes a switching system 10 which provides telephone services to user terminals 17 which are connected to switching system 10 by telephone lines 15. Switching system 10 interconnects terminals 17 with each other and with the remainder of the telephone system, designated in FIG. 1 as network 18, to which the switching system 10 is connected by telephone trunks 16. Network 18 typically comprises one or more other switching systems 10 and user terminals 17.

The telephone system of FIG. 1 implements one or more network numbering plans. Network numbering plans are well known in the art. An illustrative example thereof is the North American network numbering plan of the North American public telephone system. A network numbering plan is a convention that allows users to use symbols (e.g., dialed digits) to define to the network the treatment that they wish a call to receive. The generic characteristics of network numbering plans are graphically illustrated in FIG. 2. As shown, a network numbering plan 100 is composed of a plurality of defined symbol strings 101-150. Each defined symbol string consists of one or more symbols, and has a defined meaning. Illustrative examples of symbol strings are: area codes, office codes, extension numbers, long distance carrier codes, and feature specification codes. The defined symbol strings are building blocks from which symbol sequences 151-199--e.g., network numbers, dialed numbers--are constructed. Each valid symbol sequence consists of one or more defined symbol strings, and has a meaning within the network numbering plan. A symbol sequence defines the treatment that a corresponding call is to receive. If a symbol sequence is valid (i.e., does not violate the definitions of its constituent symbol strings and their permissible contexts) it is said to be included in the network numbering plan.

Conventionally in a network such as that shown in FIG. 1, a switching system such as system 10 would understand only one numbering plan, which is used in the portion of the system of FIG. 1 that it is a part of. The switching system would transport signals pertaining to other numbering plans, used in other portions of the system of FIG. 1, to those portions for their use through communication paths that it would establish on the basis of its own numbering plan.

Switching system 10 is a stored-program controlled system, such as the AT&T Definity® G2 PBX. It comprises a conventional switching fabric 13, a processor 11 for controlling the operation of fabric 13, and a memory 12 for storing programs for execution and data for use by processor 11 in performing its control functions. It further comprises conventional service circuits 14--such as dialed-digit collection registers, outpulsing circuits, tone generators, etc.--also operating under control of processor 11 and connected to fabric 13 for use in setting up call connections and providing call features and other telecommunications services to user terminals 17.

Contents of memory 12 that are relevant to this discussion are shown in FIG. 3. Most of the programs and data structures held by memory 12 are conventional. These include an outpulsed signal-collection program module 201, a connection-establishment program module 202, a time-of-day program 203, translations and status 204 for, e.g., trunks 16, lines 15, and terminals 17, feature program modules 205, and a scratchpad memory portion 250 for holding call records 271 of individual calls. However, according to the invention, there is provided a new call-processing arrangement, referred to as world-class-routing (WCR) 200, which translates user-provided call-destination addresses or feature-selection codes--digits and other symbols that are received across telephone lines 15 from user terminals 17 or across trunks 16 from other switching systems--into call routes and feature-access connections for establishment by switching fabric 13 and network 18 and provisioning by modules 205 and circuits 14. World-class routing 200 receives, as its input, symbol-representing signals that have been outpulsed at a terminal 17 or at the other end of a trunk 16 and collected by a conventional outpulsed signal-collection module 201. It transforms the received signals into route-identifying, feature-identifying, and other connection-identifying and function-identifying information and into destination-identifying outpulsed digits, and sends these as its output to, e.g., a conventional connection-establishment program 202 or a feature module 205.

World-class-routing 200 implements the concept of a network numbering plan as being a language, in the mathematical/computer science sense. As such, world-class routing 200 defines any network numbering plan in terms of a grammar and a syntax of symbol strings that constitute the network numbering plan, and derives meaning from sequences of symbols received over lines 15 and trunks 16 by parsing those symbol sequences and analyzing the parsed symbol sequences through use of the defined grammar and syntax. Consequently, through the expedient of redefining the grammar and/or the syntax, world-class-routing 200 modifies or redefines the existing numbering plan or adapts to a totally different numbering plan.

World-class routing 200 has a modular construction, and comprises four self-contained but cooperating modules: a network digit analysis (NDA) module 210, shown in FIGS. 4-13 and 23-24; a generalized route-selection (GRS) module 220, shown in FIGS. 16-19; a digit-modification (DM) module 230, shown in FIGS. 14-15; and a digit-sending (DS) module 240, shown in FIGS. 20-22. Briefly, world-class routing 200 functions as follows.

Network digit analysis 210 implements the syntax and grammar of one or more network numbering plans. It functions as a parser and analyzer of received symbol sequences received from outpulsed signal-collection program 201, and uses the syntax and grammar to perform the parsing and analysis functions. Hereinafter, for convenience, the symbols are referred to individually as dialed digits, and collectively the received symbol sequence is referred to as a dialed number. Analysis may show that a tone needs to be returned to the source of the dialed number. For this purpose, network digit analysis 210 has a connection to a tone-generation facility 262, which is illustratively one of the service circuits 14. Analysis may also show that the dialed number may need to be modified and then re-analyzed; for this purpose, network digit analysis 210 depends upon digit modification 230 to perform the requisite modifications. The result of the analysis is a resultant dialed number, an index (VNI) for an endpoint or feature that the caller is trying to reach, and permissions information for the call. Network digit analysis 210 supplies these to generalized route selection 220.

Generalized route selection 220 determines the feature or best-choice route to be used for the call. It uses the endpoint identifier and information obtained from time-of-day program 203 and translations and status 204 to convert the received identifier into a feature number or a routing pattern number, and then uses the pattern number to select a trunk group over which the call is to be routed. The results of the functions of generalized route selection 220 are either an invocation of a feature module 205, or a digit sending index, a selected trunk group, and information on signaling characteristics. Generalized route selection 220 supplies the route-relating results to digit sending 240.

Digit sending 240 uses the digit sending index to retrieve further information on call-establishment signaling characteristics, and then uses the full complement of the received information to define the control signals which are to be outpulsed. It makes use of digit modification 230 to convert the resultant dialed number into an outpulsed number for outpulsing. Digit sending 240 then causes connection-establishment program 202 to establish a requisite connection having the requisite characteristics over the selected trunk.

The total collection of received outpulsed control signals consists of the dialed number which may or may not be preceded by a network dial-access code (DAC). The dial-access code identifies the network that the user is attempting to reach. The absence of a dial-access code is interpreted as the selection of a default network. For example, it is common in many private multi-premise networks to initially dial a "9" or an "8" to respectively signal a desire to use the public telephone network or a private network; the absence of the "9" or "8" indicates that the dialed number refers to an extension or feature on the receiving switching system 10 itself, commonly referred to as the internal dialing plan. Or, in the public network, it is common to initially dial a "10XXX" to designate which inter-LATA carrier's network the user is trying to reach; in the absence of the "10XXX" prefix, the call is routed to a default carrier's network. In the above examples, the "9", "8", and the "10XXX" serve as the dial-access codes. Initially, network digit analysis 210 merely converts the dial-access code or its absence into a network number which identifies to network digit analysis 210 the network which the user is attempting to use. But more commonly, this conversion may be done by a separate internal dial plan program (not shown) that may be used to interface outpulsed signal-collection program module 201 to network digit analysis 210. Every network may use a different numbering plan each having its own grammar and syntax, and hence the network number identifies to network digit analysis 210 the numbering plan that should initially be used in analyzing the dialed number.

The data structures of network digit analysis (NDA) 210 are shown in FIGS. 4-8 and 23-24. Network digit analysis 210 includes a plurality of network syntax trees 320. A network syntax tree 320 is a data structure whose records are organized in a hierarchical tree structure. Each network number has its own network tree 320 associated therewith. The records of a network tree 320 define the syntax of the network's dialing plan. Each network tree 320 has three types of records: a network root 310, branch nodes 311, and leafs 312. Records 310-312 are hierarchically interconnected by paths 313. Network root 310 is the entry point into network tree 320. Branch nodes 311 and leafs 312 lie in a plurality of hierarchically-organized levels that subtend network root 310. Each branch node 311 is merely a decision point within a network tree 320. Which branch node 311 within network tree 320 is reached is a function of the dialed digits. Likewise, the path 313 that is taken out of that node 311 is a function of the following dialed digits. This may include a "wild card" path 313, which is taken either when no other path 313 is specifically defined for the particular dialed digit or when subsequent dialed digits render the specifically-defined path invalid. This allows for a "default" string identifier, where no specific digits are administered for the "default" string. Each path 313 from a node 311 terminates either in another branch node 311 or in a leaf 312. The particular set of dialed digits that results in a leaf 312 being reached is referred to as a string identifier. In other words, a string identifier consists of the dialed digits that are used to traverse a network tree 320 from network root 310 to leaf 312. For example, in FIG. 4, the string identifier of the leaf 312 shown on the right-hand side of the figure is "PNC". This may illustratively correspond to a particular area code in the North American public network numbering plan.

The string identifier forms the most-significant digits of a digit sequence referred to as a string. Strings are digit, or other symbol, sequences that are defined for, i.e., that have a meaning within, a network numbering plan. Thus, they are the constituent members of the network numbering plan. Each leaf 312 defines a swing. Hence, each defined string has its own associated leaf 312.

As shown in FIG. 5, a leaf 312 is implemented as a database record that holds information entries 330-339 that define the associated string. The information entries held by each leaf 312 include: resolution 330, string type 331, string length 332, restart analysis 333, virtual nodepoint index (VNI) 334, continue collection option 335, tone option 336, unauthorized call control facilities restriction level (UCC FRL) 337, freeze VNI option 338, and combine VNI option 339.

Resolution 330 specifies whether leaf 312 corresponds to a call route-specifying or to a call feature-specifying string. String type 331 holds a number that identifies the string type. In the illustrative example of the North American public network numbering plan just given, string type 331 would hold a number that identifies this string type as an area code. String type 331 serves as as an interface to the numbering plan grammar which is defined by the data structures of FIGS. 7 and 8. That grammar defines permissible contexts of, or relationships between, (e.g., permissible combinations and sequential orderings of) the various string types.

String length 332 specifies the permissible range of the length of the string, by specifying the maximum and minimum length-range boundaries. String length is permitted to be any range that includes (is equal to or greater than in this illustrative example) the length of the string identifier. In the illustrative example of the North American public network numbering plan just given, string length 332 would specify the same minimum and maximum length-range boundaries corresponding to a fixed string length of 10 digits (area code--3, plus office code--3, plus subscriber number--4).

Restart analysis 333 holds information that interfaces, or relates, different numbering plans to each other. It holds a digit modification index (DMI) that specifies how the dialed digits of the string should be modified. Digit modification 230 does the actual modifying, and DMI serves as a pointer to a digit modification table entry (see FIG. 14) that specifies the digit modification to be performed. Restart analysis 333 also identifies the network of re-analysis, i.e., the network number whose network tree 320 is to be used to re-analyze the string following its modification. Restart analysis 333 further specifies whether the modified string is or is not to be re-analyzed; the former is the normal condition. In the illustrative example of the North American public network numbering plan just given, if the specified area code corresponds to a private network that internally uses 7-digit numbers, restart analysis 333 holds a DMI that points to the appropriate 10-to-7 digit conversion algorithm, identifies the network number that corresponds to the subject private network, and specifies that re-analysis is to be performed.

VNI 334, the virtual nodepoint index, specifies call-feature or network-routing information for the string, in terms of an index which is used by generalized route selection 220 to find either a feature or a route for the call. It is part of an expression of the string's influence on selection of a feature or a route for the call.

Continue collection 335 indicates whether or not any additional string will or will not follow this string in the sequence of dialed numbers, by indicating whether outpulsed digit collection (performed by function 201) is to stop or is to continue after receipt of this string.

Tone 336 indicates the type of tone or other caller-perceivable signal, if any, that is to be returned as feedback to the outpulsing entity (e.g., to a user at a terminal 17) following the receipt of this string.

UCC FRL 337 specifies the permissions level that a user must have in order to be allowed to access the endpoint or service that corresponds to the string. It may be used, for example, to block certain users' access to 900-type numbers.

Freeze VNI option 338 indicates if this string is the route-determining/feature-determining string of the dialed number. If so, the VNIs of any other strings that follow this string in the dialed number will be discarded. This will be true even if freeze VNI option 338 of any of these following strings is set. It is also a part of the expression of the string's influence call feature or route selection.

Combine VNI option 339 indicates whether or not--and if so, how--the VNI of this string should be combined with the VNIs of strings that preceded this string in the dialed number. Combine VNI option 339 thus allows route selection to be progressively impacted based upon the particular strings that are identified. While any function could conceivably be employed to combine VNIs, concatenation and addition are most likely to be used. It is also a part of the expression of the string's influence on call feature or route selection.

As string length entry 332 implies, strings may be of different length, i.e., be composed of different numbers of digits. Hence, different paths 313 extending from a branch node 311 may be reached by the same dialed digit, and which path 313 is reached by the dialed digit is a function of the number of digits that were dialed. For example, as shown in network tree 320 which corresponds to network number 300, both "AB" and "ABCD" may be defined strings. Whether the second dialed digit "B" reaches a leaf 312 that defines one of the strings "AB", or merely reaches a branch node 311 that is on the path to the leaf 312 that defines the string "ABCD", is a matter of what, if anything, is dialed after the digit "B ". This will be explained more fully below.

Also, identical strings may be defined in a plurality of network trees 320. Furthermore, the identical string may have the same definition or different definitions in a plurality of trees 320.

It is by means of a network syntax tree 320 that the syntax of a numbering plan is defined. To define the syntax of a numbering plan, a system administrator merely creates a network tree 320 and populates its leaf entries 330-339. To modify or expand an existing numbering plan, the system administrator merely adds branch nodes 311 and leafs 312 to network tree 320, or changes the dialed digits that correspond to particular paths 313 within network tree 320, or merely changes the information stored in one or more entries 330-339 of one or more leafs 312. The structure is completely flexible, allowing an administrator to provide any number of records that may be needed. As branch-defining and leaf-defining memory resources are needed, they are removed from a common pool of database records that represent branches and leaves, so that each network dial plan can be as complex or as simple as is necessary while using memory resources most efficiently.

The tree structure makes the analyzing of dialed digits very simple. The dialed digits are merely used one-by-one to index from root 310 down tree 320, until one or more leafs 312 are reached. The reaching of a leaf 312 means that a string in the dialed number possibly has been identified. The strings defined by the reached leaves 312 are referred to as "candidates". Candidates are checked against grammar rules defined by the data structure of FIG. 7 to determine their suitability. Subsequent dialed digits are used to select between multiple reached leaves 312. Once a single candidate leaf 312 has been selected, any subsequent dialed digits are considered to be a part of a next separate string, and the indexing process is repeated. Hence, no sorting or searching is required for digit analysis. Rather, only a predetermined maximum number of record reads--corresponding to the maximum string identifier length--is required to reach an analysis endpoint, thereby guaranteeing that the parse of any symbol string will be effected in a known maximum time period. If the numbering plan is such that leading dialed digits of numerous dialed numbers tend to be repeated (e.g., an area code and an office code might both be the same sequence of the same three digits), the storage is non-duplicative and hence is very compact. Also, string identifiers never need to be explicitly stored, thereby conserving memory space. Rather, dialed digits merely act as pointers to a sequence of database records.

In addition to having an associated network syntax tree 320, each network number has an associated exception forest 350, shown in FIG. 6. Exception forests 350 serve to identify exceptions to the string definitions found in leafs 312 of network syntax trees 320. Each exception forest 350 includes one or more exception syntax trees 360. Each exception syntax tree 360 is structured identically to a network tree 320 (as shown in FIG. 4). As with network trees 320, the network number serves to identify the corresponding exception forest 350. For efficient access, desired exception tree 360 is identified by a string type and a string length. The string type and string length which are used to index into an exception forest 350 are the contents of entries 331 and 332 of a candidate leaf 312 that has been found in network tree 320 to correspond to the string that is being analyzed.

As has already been mentioned, network digit analysis 210 further includes separate data structures that define the grammar of the network numbering plan. These are shown in FIGS. 7-8 and 23-24. Each network number has its own sequence grammar matrix 400 of FIG. 7 and combine grammar matrix 410 of FIG. 8. Each matrix 400 (410) comprises a plurality of rows 401 (411) and columns 402 (412). Each row 401 (411) corresponds to a different one of the defined string types (331 of FIG. 5) for the network dialing plan, as does each column 402 (412). Hence, the number of rows 401 (411) and columns 402 (412) depends upon the number of defined string types. The intersection of a given row 401 (411) and column 402 (412) forms an entry 405 (entries 415 and 416) whose contents define permissible contexts or relationships between the corresponding string types.

On the one hand, an entry 405 of sequence grammar matrix 400 formed by an intersecting row 401 and column 402 defines whether the string type that corresponds to the column 402, referred to as next-received string type 404, is allowed to follow in a dialed number the string type that corresponds to the row 401, referred to as last-received string type 403. Matrix 400 thus defines permissible sequential ordering of string types within dialed numbers. The filled-in sequence grammar matrix 400 shown in FIG. 7 is illustratively populated with information that applies to the North American public network numbering plan, while the sequence grammar matrix 400 shown in FIG. 23 is illustratively populated with information that applies to the internal numbering plan of switching system 10.

On the other hand, first entry 415 of combine grammar matrix 410 formed by an intersecting row 411 and column 412 defines whether VNI 334 (see FIG. 5) of the string type that corresponds to the column, referred to as received string type 414, is allowed to be combined with VNI 334 of the string type that corresponds to the row, referred to as retained string type 413. And second entry 416 formed by the same row 411 and column 412 as first entry 415 defines the string type that is retained and associated with the combined VNI. The string type defined by second entry 416 becomes the next retained string type 413. Matrix 410 thus defines string-type combinations that can share in defining a call feature or call route. The topmost combine grammar matrix 410 shown in FIG. 8 is illustratively populated with string types of the North American public network numbering plan. For this particular plan, entries 415 take on the same values as corresponding entries 405 of sequence grammar matrix 400 of FIG. 7, whereas entries 416 take on the values of the received string type 414. The combine grammar matrix 410 shown in FIG. 24 is illustratively populated with string types of the internal numbering plan of FIG. 23. For this plan, entries 415 also take on the same values as corresponding entries 405 of sequence grammar matrix of FIG. 23, and entries 416 take on the values of the received string type 414.

An alternative implementation of FIG. 8 may have a plurality of combine grammar matrices 410 for each network number, one for each combinational function specifiable by combine VNI options 339 of leafs 312 of network syntax tree 320 for that network number.

The functionality of network digit analysis 210, including the use of the data structures of FIGS. 4-8 and 23-24, is illustrated in FIGS. 9-12. Network digit analysis 210 includes two functions: a string-identification function 340 diagrammed in FIGS. 9-12, and a string-action function 341 diagrammed in FIG. 13.

String-identification function 340 identifies a string based on the dialed digits, string length, and string context (the identity, string type, of any preceding strings). It is used to recognize (e.g., identify and validate) all strings of a dialed call-control symbol sequence. It is initially invoked for a call at step 500 in response to receipt of collected digits from program 201. Function 340 accesses call record 271 (see FIG. 3) of the call to obtain stored information about the call, at step 502. Upon initial invocation of function 340 for a call, that call's record 271 is empty. No dialed digits have previously been received and stored for the call, so step 504 is a null step, and function 340 proceeds to step 506.

As was mentioned above, the dialed digits are accompanied either by a dialed access code or by a network number, and function 340 first determines from the received information the network number that is to be presently used and stores it in network number entry 252 of call record 271, at step 506. Function 340 then applies the set of dialed digits obtained at step 504 to network tree 320 that corresponds to the determined network number, at step 508. Function 340 uses the dialed digits one-by-one to select and traverse paths 313 of network tree 320. As function 340 traverses paths 313 of tree 320, it populates a stack 251 of call record 271 (see FIG. 3) for this call with candidates for the strings' identity, putting them on stack 251 in the order of their lexicographic matchability, at step 510. In other words, function 340 traverses paths 313 of tree 320 based upon the dialed digits, searching for leaves 312. Any leaves 312 that it encounters during its traverse, it places on stack 251, in the order in which they were encountered. Stack 251 is a conventional last-in, first-out buffer data structure created on a per-call basis. The most generic leaves 312, offering the most loosely-fitting definitions, are encountered first in network tree 320, so they are placed at the bottom of stack 251, while more specific leaves 312, offering the more precise definitions, are encountered later in network tree 320 and so they are placed closer to the top of stack 251. Function 340 continues to traverse network tree 320 until it either reaches a leaf 312 at the end of every possible path or until it runs out of dialed digits, whichever is first. For example, referring to FIG. 4, if the presently-used network number is "a" and the received dialed digits are "ABC", following step 510, stack 251 contents include, from the bottom of stack 251 up, the two leaves 312 reached by digits "AB", and intermediate node 311 reached by digits "ABC". On the other hand, if the received dialed digits are "ABCDE", stack 251 contents include the two leaves 312 reached by digits "AB", and leaf 312 reached by digits "ABCD". As to which of the two leaves 312 reached by digits "AB" would be lowest on stack 251 is determined by the contents of their respective string length entries 332: the shorter the string length, the more generic the definition. Hence, the leaf 312 specifying the shorter string length would be placed lower on stack 251. Function 340 also places on stack 251 any branch nodes 311 that it has reached upon running out of received dialed digits.

Returning to FIG. 9, following step 510, function 340 initializes a number-of-digits-needed entry 258 of call record 271 to some high number, e.g., infinity, at step 514. Function 340 then proceeds to candidate selection activities, at steps 516 et seq. Function 340 accesses stack 251 and retrieves therefrom the top stack entry, at step 516. If no stack entry is available because stack 251 is empty, as determined at step 518, function 340 checks a candidates-remain flag 259 of call record 271, at step 520. This flag indicates whether there is any further possibility of a string definition being found for the received dialed digits. Flag 259 is initially cleared for a call, resulting in a negative answer at step 520. Function 340 therefore causes the call to be given default treatment, such as return of a reorder tone to the caller, at step 522. Call-processing functions for the call are thus completed, and function 340 exits, at step 524.

Returning to step 518, if stack 251 is not empty, function 340 checks the retrieved top stack entry to determine whether it is a leaf 312 or a branch node 311, at step 526. If the retrieved stack entry is a branch node 311, function 340 determines from network tree 320 the number of digits that are needed to reach the nearest leaf 312 from that branch node 311, at step 528. Function 340 then compares this number against contents of number-of-digits-needed entry 258 of call record 271, at step 530. If the determined number is smaller than the contents of entry 258, function 340 sets contents of entry 258 to the determined number, at step 532. Following step 532, or if the check at step 530 shows that the determined number is not smaller than the contents of entry 258, function 340 discards the retrieved stack entry, at step 536, and returns to step 516 to retrieve the next stack 251 entry.

Returning to step 526, if the retrieved stack entry is a leaf 312, function 340 checks whether string type 331 of retrived leaf 312 satisfies the requirements of the sequence grammar, at step 534. Function 340 performs this check by accessing sequence grammar matrix 400 of the network number held by network number entry 252 of call record 271. Function 340 then applies contents of string type 331 of retrieved leaf 312 as next-received string type 404 to that matrix 400, and applies the contents of a last-received string type entry 255 of call record 271 as a last-received string type 403 to that matrix 400. Function 340 then examines the corresponding entry 405 of matrix 400 to determine whether it contains an affirmative or a negative response. If list-received string type entry 255 is empty, this string is the first string to be received for the call, and so the requirements of the sequence grammar must be satisfied thereby. Therefore, any candidate string corresponding to a subscriber number would be discarded in the case of the North American numbering plan. If the response obtained at step 534 is negative, function 340 discards retrieved leaf 312, at step 536, and proceeds to step 516 to retrieve the next stack entry. But if the response obtained at step 534 is affirmative, function 340 proceeds to the steps of FIG. 11.

Returning to step 520 of FIG. 9, if function 340 finds candidates-remain flag 249 of call record 271 set, it proceeds to the steps of FIG. 10. Function 340 checks whether contents of number-of-digits-needed entry 258 of call record 271 is zero, at step 580. If so, function 340 sets a short (e.g., 3 second) inter-digit timer 261 associated with outpulsed signal-collection module 201 (see FIG. 3), at step 582, and directs module 201 to collect one digit, at step 584. If contents of entry 258 are not found to be zero at step 580, function 340 sets a long (e.g., 10 second) inter-digit timer 260 associated with outpulsed signal-collection module 201 (see FIG. 3), at step 586, and directs module 201 to collect the number of digits indicated by contents of entry 258, at step 588.

Timers 260 and 261 indicate to program 201 the maximum amount of time that is allowed to elapse between the dialing of individual digits by a user. Long inter-digit timer 260 is set at times when the user's failure to dial more digits would result in a logical error and hence the giving of default treatment to the call. Conversely, short inter-digit timer 261 is set at times when it is permissible for the user to have completed dialing, and therefore it is not desirable to wait for the long period of time before responding to the user's input.

Following step 584 or 588, function 340 stores the previously-received dialed digits in dialed digits entry 253 of call record 271 for future use after the requisite number of digits has been collected and returned by module 201, at step 590. Function 340 then returns, at step 592.

Module 201 responds to the digit-collection request by attempting to collect the requested number of digits. If long inter-digit timer 260 has been set and collection of more than one digit was requested, upon the receipt of each digit, module 201 resets long inter-digit timer 260. If program 201 collects the requested number of digits without the set one of the inter-digit timers 260 and 261 having expired, it re-invokes function 340 at step 500 of FIG. 9 and passes it the additional collected digit or digits. If long inter-digit timer 260 expires prior to program 201 having collected the requested number of digits, program 201 re-invokes function 340 at step 500 and passes it whatever number of digits it has collected along with notification that long timer 260 timed out. If short inter-digit timer 261 has been set and expired prior to module 201 having collected the requested one dialed digit, module 201 re-invokes function 340 and returns a notice of short timer 261 timeout.

Returning to FIG. 9, upon its re-invocation at step 500, function 340 retrieves call record 271, at step 502, and concatenates any just-received collected digit or digits with the previously-received collected digits for the call which it had stored in entry 253 at step 590 of FIG. 10. Function 340 then proceeds to steps 506 et seq. to re-populate stack 251 with candidates for the string definition and to try and select a candidate therefrom.

Returning to step 534, if the check there reveals that string type 331 of leaf 312 that has been retrieved from stack 251 does satisfy the requirements set forth in sequence grammar matrix 400 of FIG. 7, function 340 proceeds to the steps of FIG. 11. Function 340 first checks whether the dialed digits could possibly satisfy the retrieved leaf's length requirement as specified by string length 332 of that leaf 312, at step 550. This determination is made by checking whether the number of received dialed digits falls within or exceeds the range specified by string length 332, or whether the number of received dialed digits falls below the range specified by string length 332 but no indication has been received that outpulsed digit collection has ended (such as the caller having dialed an "end-of-dialing" signal, e.g., a "#"). If it is determined that the dialed digits could not possibly satisfy the leaf's length requirements, function 340 returns to step 536 of FIG. 9 to discard the retrieved leaf 312 and then proceeds to step 516 to retrieve the next stack entry.

If it is determined at step 550 that the dialed digits could possibly satisfy the retrieved leaf's length requirements, function 340 checks whether the dialed digits do in fact satisfy those requirements, at step 552. This determination is made by checking whether the number of received dialed digits falls within or exceeds the range specified by string length 332 of retrieved leaf 312. If not, function 340 determines how many additional digits are required to satisfy the leaf's string length requirements, at step 554, and compares this number with the contents of number-of-digits-needed entry 258 of call record 271, at step 556. If the number of additional digits needed to satisfy the leaf's length requirements is smaller, function 340 sets contents of number-of-digits-needed entry 258 to that number, at step 558. Following step 558, or if the number of additional digits needed to satisfy the leaf's length requirements is not smaller than the contents of entry 258, function 340 sets candidates-remain flag 259 of call record 271, at step 560, and then returns to step 536 of FIG. 9 to examine other stack 251 entries.

Returning to step 552, if it is determined that the dialed digits do satisfy the leaf's length requirements, function 340 checks, at step 562, whether it had received a notice of long inter-digit timer 260 timeout at its invocation. If so, function 340 proceeds to FIG. 12. If the answer to the check at step 562 is "no", function 340 checks, at step 564, whether it had received a notice of short inter-digit timer 261 timeout at its invocation. If so, function 340 checks, at step 566, whether the number of dialed digits exactly equals the length requirement of the retrieved leaf 312. The only way that the number of dialed digits can exactly equal the length requirement is if the string-length range specified by string length 332 of retrieved leaf 312 is one and its range boundaries equal the number of dialed digits. If the answer at step 566 is "yes", function 340 proceeds to FIG. 12. If the answer is no, function 340 returns to step 536 of FIG. 9.

Returning to step 564, if it is there determined that function 340 was not invoked in response to timeout of short inter-digit timer 261, function 340 checks whether candidates-remain flag 259 of call record 271 is set, at step 568. If not, function 340 proceeds to FIG. 12; if so, function 340 sets contents of number-of-digits-needed entry 258 of call record 271 to zero, at step 570, and then returns to step 536 of FIG. 9.

Turning to FIG. 12, it shows the activities that string identification function 340 performs to determine whether an exception tree 360 candidate leaf should be substituted for candidate leaf 312 selected from network tree 320. Function 340 uses the network number stored in network number entry 252 of call record 271 to select an exception forest 350 (see FIG. 6), at step 800. It then uses string type 331 and string length 332 entries of selected candidate leaf 312 to select an exception tree 360 from selected exception forest 350, at step 802. Finally, function 340 applies the string of received dialed digits to selected exception tree 360, at step 804, in the same manner as was described for step 508 of FIG. 9, to determine if tree 360 contains an exception leaf 312 that corresponds to this string, at step 806. If there exists an exception leaf 312 that corresponds to this string, function 340 selects it as the candidate for the string instead of leaf 312 that had been selected in FIGS. 9-11, at step 808. Following step 806 or 808, function 340 stores contents of string type 331 of whichever leaf 312 is selected in last-received string type entry 255 of call record 271, at step 810. Function 340 then invokes string-action function 341 of FIG. 13, at step 812, passes to it the presently-used network number, the string, and the selected leaf 312, and returns, at step 814.

Upon being invoked, at step 900 of FIG. 13, string-action function 341 examines entries 330-339 of the received leaf 312 to determine what needs to be done, at step 902. If a feedback signal (tone in this example) is specified by tone entry 336 to be given to the user, at step 904, function 341 causes a tone generation 262 service circuit (see FIG. 3) to give the specified tone to the user, at step 906. If restart analysis entry 333 of leaf 312 contains a digit modification index (DMI), it indicates that digit modification is specified, at step 908, so function 341 invokes digit modification 230, at step 910. As part of the invocation, function 341 passes to digit modification the received string, and the DMI from entry 333 of received leaf 312. Function 341 then awaits the receipt of the digit-modification result, at step 912.

Digit modification 230 comprises a data structure shown in FIG. 14 and a function shown in FIG. 15. The data structure is a table 1000 of entries 1001 which are accessed by a received DMI 1020. Each entry comprises three fields 1010-1012. Delete digits range field 1010 specifies the range of digits, if any, in terms of digit positions within the received string, which is to be deleted from the string. Insert digits range field 1011 specifies the range of digits, if any, in terms of digit positions within the received string, which are to be inserted, and insert digits field 1001 specifies the actual digits that are to be inserted.

Upon its invocation, at step 1100 of FIG. 15, a digit modification function 342 uses DMI 1020 which it received as part of its invocation to find and access a particular entry 1001 of table 1000, at step 1102. It then performs the modifications specified by the accessed entry 1001 on the string which it received as part of its invocation, at steps 1104 and 1106. Function 342 then returns the modified received string to whoever requested the modification, at step 1108, and exits, at step 1110.

Returning to FIG. 13, function 341 receives the modified string, at step 914, and stores it in dialed digits entry 253 of call record 271 instead of the string that it had received at step 900, at step 916.

If restart analysis entry 333 of candidate leaf 312 does not contain a DMI, as determined at step 908, or following storage of the modified string at step 916, string action function 341 proceeds to steps 918 et seq. to calculate a VNI for the call. Function 341 checks if a "frozen" indicator 257 of call record 271 of the call (see FIG. 3) has been set, at step 918. If so, computation of the VNI for the call has been frozen, so no VNI calculation remains to be done and function 341 proceeds to steps 950 et seq. If the call record's "frozen" indicator 257 is not set, function 341 checks combine VNI entry 339 of the received leaf 312 to determine if it is set, at step 930. If it is also not set, function 341 stores the contents of VNI entry 334 of leaf 312 in call VNI field 254 of call record 271, at step 934, discarding in the process any VNI that has previously been stored in VNI field 254. Function 341 also stores the contents of string type entry 331 of leaf 312 in retained string type field 255 of call record 271, at step 946. Function 341 then proceeds to step 948.

Returning to step 930, if combine VNI entry 339 of candidate leaf 312 is set, function 341 checks whether the combine grammar allows the combining to be done, at step 932. Function 341 performs this step by accessing combine grammar matrix 410 (see FIG. 8) of the network number held by network number entry 252 of call record 271. Function 341 then applies contents of string type 331 of the received leaf 312 as a received string type 414 to that matrix 410, and applies the contents of retained string type entry 256 of call record 271 as a retained string type 413 to that matrix 410. Function 341 then examines the corresponding entry 415 of matrix 411 to determine whether it contains an affirmative or a negative response. If retained string type entry 256 of call record 271 is empty, this string is the first string to be received for the call, and so combining is always disallowed, as there is nothing to combine with. If the response obtained at step 932 is negative, function 341 proceeds to step 934. If the response obtained at step 932 is affirmative, function 341 combines any VNI stored in VNI field 254 of call record 271 with contents of VNI entry 334 of received leaf 312 in the manner specified by combine VNI entry 339, at step 940. Function 341 then stores the resultant VNI in VNI field 254 of call record 271, at step 942, discarding in the process the previous contents of VNI field 254. Function 341 also retrieves the new string type that is to be retained and associated with the VNI produced at step 940, at step 944. Function 341 performs this step by proceeding as for step 932, but instead of examining entry 415, it accesses the corresponding entry 416 to obtain therefrom the retained string type. Function 341 then stores the retrieved retained string type 416 in retained string type entry 256, at step 945, and then proceeds to step 948.

At step 948, function 341 checks freeze VNI entry 338 of received leaf 312 to determine if its indicator is set. If so, it means that VNIs of subsequently-received strings are not to affect the call's VNI. Function 341 therefore sets "frozen" indicator 257 of call record 271, at step 949, to prevent contents of call VNI entry 254 from being changed. Function 341 then proceeds to step 950. If freeze VNI entry 338 of received leaf 312 is not set, function 341 proceeds directly to step 950.

At step 950, function 341 checks whether restart analysis entry 333 of received leaf 312 indicates that the modified string obtained at steps 912-914 is to be re-analyzed. If so, function 341 checks whether restart analysis entry 333 specifies a new network number, at step 952. If so, function 341 stores this new network number in network number field 252 of call record 271, at step 954. Following step 954, or if a new network number is not specified at step 952, function 341 re-invokes string identification function 340, at step 958, passing it back the modified string, any new network number, and any indication that dialing has been completed. Function 341 then returns to the point of its invocation, at step 960.

Returning to step 950, if it is found there that re-analysis is not to be performed, function 341 checks, at step 970, whether continue collection entry 335 of received leaf 312 indicates that the just-received string is to be followed by another string in the dialed number. If so, the job of network digit analysis is not yet done, and function 341 re-invokes outpulsed signal-collection module 201 to prompt it to collect more digits, at step 974. But if entry 335 indicates that the just-received string is not to be followed by another string in the dialed number, the job of network digit analysis 210 is done, and function 341 invokes generalized route selection 220, at step 972, and passes it the modified dialed number now stored in dialed digits entry 253 and the call VNI entry 254 of call record 271. Following step 974 or 972, function 341 exits, at step 976.

Generalized route selection (GRS), 220 is shown in FIGS. 16-19. The data structures of GRS 220 are shown in FIGS. 16-18. GRS 220 includes a pair of multi-dimensional (in this illustrative example, four-dimensional) matrices 1200 and 1202 of FIG. 16. Route matrix 1200 is populated with routing pattern numbers 1201, while feature matrix 1202 is populated with feature numbers 1203. The index into matrices 1200 and 1202 is a multi-element entity having one element for each matrix dimension. For the example of four-dimensional matrices of FIG. 16, the matrix index illustratively comprises: call VNI 254, a time-of-day routing plan 1230, a conditional routing count 1231, and a tenant partition 1232. Call VNI 254 is obtained by GRS 220 from NDA 210. Time-of-day routing plan 1230 is conventional and is obtained by GRS 220 from a conventional time-of-day program 203 (see FIG. 3). Conditional routing count 1231 is also conventional and is obtained by GRS 220 either as a trailing digit to a dialed number from an incoming call trunk 16, or from translations 204 (see FIG. 3) that are associated with the trunk group of an incoming call trunk 16 or terminal line 15. Tenant partition 1232 is likewise conventional, and is obtained by GRS 220 from translations 204 that are associated with calling station 17 or incoming call trunk 16. Call VNI 254 is determinative of which one of the two matrices 1200 and 1202 is accessed by the index. Any desired contextual parameters may be used as elements of the multi-dimensional matrix.

A feature number 1203 obtained for a call from feature matrix 1202 identifies the one of feature modules 205 (see FIG. 3) which should be invoked. Alternatively, a feature number 1203 obtained from matrix 1202 may be used as an element of an index into feature pattern tables, similarly to how routing pattern numbers 1201 are used, as described below.

A routing pattern number 1201 obtained for a call from matrix 1200 serves as a pointer to one of a plurality of routing pattern tables 1300 of FIG. 17. Each routing pattern table 1300 has a plurality of entries 1301 each one of which defines a routing preference. The routing preferences are listed in each table 1300 sequentially in the order of their relative preference. The following call characteristics illustratively serve as criteria for selecting a particular routing preference, i.e., entry 1301 of a table 1300: a facilities restriction level (FRL) 1330, a tenant partition 1232, a bearer capability 1331, a toll permission 1332, an ISDN required/preferred 1333, and a DCS required/preferred 1334. The most-preferred preference that meets these criteria and also meets the additional requirement 1335 of having a circuit free and available to carry the call, is selected for the call.

FRL 1330 is conventional and is obtained by GRS 220 either as a trailing digit to a dialed number from an incoming call trunk 16 or from translations 204 (see FIG. 3) that are associated with the originating station 17 or the trunk group of the incoming call trunk 16. Tenant partition 1232 is the same as discussed in conjunction with FIG. 16. Bearer capability 1331 is also conventional and is obtained by GRS 220 either from ISDN messaging that accompanies an incoming call on a trunk 16, or as a default value from translations 204 of either incoming trunk 16 or originating station 17. Toll permission 1332 is likewise conventional and is obtained by GRS 220 from translations 204 of originating station 17 or the incoming call trunk 16. Whether routing over ISDN facilities is required or preferred 1333 is also a conventional item of information and is obtained by GRS 220 either from translations 204 of originating station 17 or is derived from messaging that accompanies a call on the incoming call trunk 16. DCS required/preferred 1334 specifies whether a requested feature is a distributed communications feature (DCS) that requires routing over facilities providing feature transparency between switches in a network (for a description of feature transparency, see U.S. Pat. No. 4,488,004). The information is obtained by GRS from a station-to-station calling feature module. Finally, circuit availability 1335 is determined from line 15 and trunk 16 status records of translations and status 204.

Routing preference 1301 that is selected for a call on the basis of the above-described criteria defines the preferred route for the call and is used by GRS 220 to route the call. An illustrative routing preference 1301 is shown in FIG. 18. It comprises a plurality of information fields 1401-1406. Trunk group number 1401 specifies the group of trunks 16 over any one of which the call may be routed. Sending requirements 1402 specifies how called number information that will accompany the call is to be sent, such as: is a pause required before sending digits, must the system listen for dial tone before sending digits, do digits need to be grouped with pauses, and do individual digit groups get sent via dial pulses or Touch-Tone pulses. Toll information 1403 is a table of exceptions that specifies toll-free telephone numbers for this trunk group. ISDN sending format 1404 specifies which information element (IE) of ISDN messages is to be used for interexchange calls, and the kind of a number (based on CCITT specifications) that will be sent in the IE. Alternatively, both toll information 1403 and ISDN sending format 1404 may be implemented as indexes into associated tables. Digit modification index (DMI) 1405 specifies how the received dialed number is to be modified before being sent out. It is the equivalent of the DMI discussed in conjunction with restart analysis entry 333 of leaf 312 of FIG. 5. And digit sending index (DSI) 1406 is an index for use by digit sending 240 in defining additional digit sending criteria for the call. It will be discussed further in conjunction with digit sending 240.

Generalized route selection function 343 is shown in FIG. 19. Upon being invoked, at step 1500, function 343 proceeds to obtain time-of-day routing plan 1230, conditional routing count 1231, and tenant partition 1232, at step 1502. Function 343 then uses the obtained information along with call VNI 254 as a four-pronged index into multi-dimensional matrices 1200 and 1202, at step 1504, and retrieves the indexed entry 1201 or 1203 from the addressed one of the matrices 1200 and 1202, at step 1506. Function 343 then examines the retrieved matrix entry to determine whether it is a routing pattern number 1201 or a feature number 1203. If the retrieved entry is a feature number 1203, function 343 invokes the corresponding feature module 205, at step 1540, and passes it the modified dialed number that was received at step 1500. Function 343 then exits, at step 1542.

Returning to step 1507, if the retrieved matrix entry is a routing pattern number 1201, function 343 proceeds to obtain FRL 1330, bearer capability 1331, toll permission 1332, ISDN required/preferred 1333, and DCS required/preferred 1334, at step 1508. Function 343 then accesses the one routing pattern table 1300 that is pointed to by the retrieved routing pattern number 1201, at step 1510, and uses the obtained information along with previously-obtained tenant partition 1232 to search the accessed pattern table 1300 for a suitable preference 1301, at step 1512. If a suitable preference 1301 is found, as determined at step 1514, function 343 checks translations and status 204 to determine whether a circuit in that preference 1301 is available for the call, at step 1516. If no circuit is available, function 343 returns to step 1512 to search for another suitable preference 1301. If a circuit is available, function 343 retrieves the preference 1301 information, at step 1518.

Returning to step 1514, if no suitable preference 1301 is found, function 343 retrieves information defining a default preference 1301, at step 1520. Following step 1518 or 1520, function 343 checks DMI 1405 of the retrieved preference 1301 to determine if digit modification is specified thereby, at step 1522. If DMI 1405 is null, no digit modification is required, and function 343 proceeds to step 1530. If DMI 1405 is not null, digit modification is required, and so function 343 invokes digit modification function 342 of FIG. 15, at step 1524. As part of the invocation, function 343 passes to digit modification function 342 the modified dialed number that it received at step 1500 and the contents of DMI 1405. Function 343 then awaits receipt of the digit-modification result, at step 1526.

Digit modification function 342 responds in the manner discussed in conjunction with FIG. 15. When it returns a resultant dialed number to function 343, at step 1528, function 343 proceeds to step 1530.

At step 1530, function 343 invokes digit sending 240, and passes the resultant dialed number (which could be the modified dialed number received at step 1500 if no additional digit modification was specified at step 1522) and retrieved preference 1301 as parameters. Function 343 then exits, at step 1532.

Digit sending 240 is shown in FIGS. 20-22. It comprises a sending table 1700 of FIG. 20 and a digit sending function 344 of FIG. 22. Sending table 1700 has a plurality of sending entries 1701 each one of which is a set of digit-sending information. Sending entries 1701 are indexed by DSIs 1406. An illustrative sending entry 1701 is shown in FIG. 21. It comprises a plurality of fields 1801-1808. Sending number 1801 specifies the number that should be sent out instead of the received resultant dialed number; when sending number 1801 is null, the received resultant dialed number is sent. Toll prefix 1802 specifies the toll indication, if any--such as "1"--that is to be sent with the number. It also specifies whether the toll prefix is to be sent only with toll calls or with all calls. Interexchange carrier code (IXC) 1803 specifies whether the "10XXX" carrier I.D. code, if any, is to be sent out for the call. Dial-access code (DAC) 1804 specifies whether the DAC, if any, that is to be sent out for this call. DAC has been discussed above in conjunction with NDA 210. End-of-dialing character 1805 specifies, whether an end-of-dialing character, e.g., "#", is to be sent at the end of the sent-out number. Each field 1802-1805 also specifies the following options for that field's information type: do not send that information type even if it was dialed by the caller; always send the contents of the field even if that information type was not dialed by the caller; and send the information dialed by the caller if the caller dialed the information type, otherwise send the contents of the field. Group digits 1806 specifies whether--and if so, how long--pauses should be used to separate groups of sent digits, and the digit-sending mode (e.g., rotary or pulse) for those groups. ISDN message type 1807 specifies the type of ISDN message that is to be used to send the number. And traveling class mark (TCM) 1808 reflects the call's FRL and conditional routing count, and specifies the zero or more TCMs that are to be sent along with the number.

FIG. 22 charts the operation of digit sending function 344. Upon being invoked, at step 1900, function 344 uses DSI 1406 of received preference 1301 as an index into sending table 1700, at step 1902, and retrieves from table 1700 the indexed sending entry 1701, at step 1904. Function 344 then uses translations and status 204 associated with the trunk group that is specified by field 1401 of received preference 1301 to determine if it is an ISDN trunk group, at step 1906. If so, function 344 creates ISDN messages that are necessary to set up a call path according to information contained in preference 1301, and populates their information fields with information specified by sending entry 1701, at step 1908, in a conventional manner. Function 344 then causes connection-establishment module 202 to set up the desired call path by sending the ISDN messages across a trunk 16 of the trunk group specified by field 1401 of preference 1301, at step 1910, again in a conventional manner. Once the requisite call path is set up, the tasks of world-class routing 200 are completed, and function 344 exits, at step 1930.

Returning to step 1906, if the specified trunk group is not an ISDN trunk group, function 344 checks field 1806 of retrieved sending entry 1701 to determine if digits are to be grouped, at step 1920. If so, function 344 causes connection-establishment module 202 to set up the call path using a first digit group and the digit-sending mode specified by field 1806 of retrieved sending entry 1701, at step 1922, in a conventional manner, by using the information contained in preference 1301 and sending entry 1701. Function 344 then causes connection-establishment module 202 to send the remaining digit groups separated by pauses of length specified by field 1806 of the retrieved sending entry 1701 and using the specified digit-sending mode, at step 1923. Function 344 then exits, at step 1930.

Returning to step 1920, if digits are not to be grouped, function 344 causes connection-establishment module 202 to set up the call path using the digit-sending mode specified by field 1806 of retrieved sending entry 1701, at step 1924, again in a conventional manner, by using the information contained in preference 1301 and sending entry 1701. Function 344 then exits, at step 1930.

To illustrate the capability of the above-described system to provide selective external access to internal numbering plan features and feature access codes, assume the following example. In the internal numbering plan, plan "b", of switching system 10, "1000" through "2999", with the exception of "2100" through "2199", "2222", and "2333", are extension numbers of terminals 17. The feature module corresponding to VNI=100 completes calls to equipped extensions. "0" is the operator feature access code (OP; VNI=10), "*2" through "*5" are the feature access codes for the leave-word-calling (LWC; VNI=200), auto-call-back (ACB; VNI=210), call-forwarding (FWD; VNI=230), and long-distance-network-access features, respectively, and "#66" is the access code for the priority-calling feature (PRIO; VNI=270). Each feature module will prompt the caller for additional digits required by the feature. (Alternatively, world-class routing 200 can be used to prompt and collect the digits, as disclosed in applicants' U.S. application Ser. No. 07/786,323 filed Oct. 31, 1991.) "2432" is the extension of plant security for a plant served by system 10, and "2111" and "2222" are vectored directory numbers (i.e., numbers that translate into other numbers) for the call-forwarding and long-distance-network-access features. Also assume that the network numbering plan, plan "a", of network 18 is the North American numbering plan and includes the long-distance network numbering plan, wherein "911" is an emergency-services access number, "744-1111" is the number of the local police department, and "538-1000" through "538-2999" are numbers assigned to switching system 10 and serve, with the exception of "538-2100" through "538-2199", "538-2222", and "538-2333", as the network numbers for terminals 17 which have the corresponding last four digits as their extension numbers in the internal numbering plan of switch 10. Further assume that it is desirable to have all internal calls for emergency services or police to be connected as priority calls to plant security, and that it is desirable to provide external access to the operator, leave-word-calling, and auto-call-back features but not to the other features. Furthermore, to gain access to the leave-word-calling and auto-call-back features, an external caller either will be prompted via dial-tone to enter a security account code of "654321", or will have to be calling from a particular external ISDN terminal whose network number is "555-3689" (and whose ISDN "call SETUP" message will provide that terminal's "caller identification" of "555-3689" in the "USERINFO" information field). The latter case provides a high degree of security, because a caller cannot enter the requisite number directly. This is unlike the former case which is susceptible to theft of the security account code. Additional combinations and sequences of symbols may be provided for security, as desired by the system administrator.

To allow external access to the requisite internal features, the features are assigned feature-access codes within the external numbering plan. The feature access codes are selected from among network numbering plan numbers that are assigned to switching system 10 but that are presently not used. For example, assume that the numbers "538-2111", "538-2222", and "538-2333" are illustratively selected to serve as the network numbering plan feature access codes for the operator, leave-word-calling, and auto-call-back features of switching system 10. Further assume that switching system 10 includes a trucker location-reporting feature (TLR; VNI=250) (one which allows truckers to call in every evening to log in their present geographical location), which cannot be accessed by callers directly served by switching system 10. Hence, this feature does not have a feature access code within the internal numbering plan of switching system 10. This feature is accessed by external callers by dialing the network number "538-2150".

The above-mentioned capabilities may be illustratively implemented through inclusion in the syntax-defining data structures of FIGS. 4 and 6 of leafs 312 defined in the following Table A.

                                      TABLE A                                      __________________________________________________________________________                                   Restart                                                                        Analysis                                                                       yes/no;d.m.                                      TREE                          range & digits;                                  Type and  String     String                                                                              String                                                                             network of    Continue                                                                             Give                                                                              Freeze                                                                             Combine               Network No.                                                                              I.D. Resolution                                                                           Type Length                                                                             reanalysis                                                                              VNI  Collection                                                                           Tone                                                                              VNI VNI                   __________________________________________________________________________     SYNTAX, b    1 feature                                                                              equipped                                                                            4   no       100  no    no don't                                                                              don't                                      extension                       care                                                                               care                  SYNTAX, b    2 feature                                                                              equipped                                                                            4   no       100  no    no don't                                                                              don't                                      extension                       care                                                                               care                  SYNTAX, b    0 feature                                                                              attendant                                                                           1   no        10  no    no yes no                                         DAC               (OP) I                                  SYNTAX, b    *2                                                                               feature                                                                              FAC  2   no       200  yes   no yes no                                         type 1            (LWC)                                   SYNTAX, b    *3                                                                               feature                                                                              FAC  2   no       210  yes   no yes no                                         type 1            (ACB)                                   SYNTAX, b    *4                                                                               feature                                                                              FAC  2   no       230  yes   no yes no                                         type 1            (FWD)                                   SYNTAX, b    *5                                                                               route FAC  2   yes;del all;                                                                             0   yes   dial                                                                              no  don't                                      type 1   none;a              tone   care                  SYNTAX, b   #66                                                                               feature                                                                              FAC  3   no       270  yes   no yes no                                         type 1            (PRIO)                                  SYWAX, b    911                                                                               feature                                                                              FAC  3   yes;del all                                                                             don't                                                                               don't no don't                                                                              don't                                      type 1   #662432;b                                                                               care care     care                                                                               care                  SYNTAX, b    9 route FAC  1   yes;del all;                                                                             0   yes   dial                                                                              no  don't                                      type 1   none;a              tone   care                  EXCEPTION, b                                                                                21                                                                               route equipped                                                                            4   no        0   no    no yes no                                         extension                                                 EXCEPTION, b                                                                               2111                                                                              feature                                                                              FAC  4   no       230  yes   no Yes no                                         type 1            (FWD)                                   EXCEPTION, b                                                                               2222                                                                              feature                                                                              FAC  4   no        0   yes   dial                                                                              no  no                                         type 1                       tone                         EXCEPTION, b                                                                               2333                                                                              feature                                                                              equipped                                                                            4   no        0   no    no yes no                                         extension                                                 SYNTAX, a   911                                                                               route address                                                                             3   yes;del all;                                                                            don't                                                                               no    no don't                                                                              don't                                               #662432;b                                                                               care          care                                                                               care                  SYNTAX, a 7441111                                                                             route address                                                                             7   yes;del all;                                                                            don't                                                                               no    no don't                                                                              don't                                               #662432;b                                                                               care          care                                                                               care                  SYNTAX,a    5381                                                                              route address                                                                             7   yes;del 3 dig;                                                                          don't                                                                               don't no don't                                                                              no                                                  none;b   care care     care                      SYNTAX,a    5382                                                                              route address                                                                             7   yes;del 3 dig;                                                                          don't                                                                               don't no don't                                                                              no                                                  none;b   care care     care                      EXCEPTION, a                                                                             5382111                                                                             route address                                                                             7   yes;del all;                                                                            don't                                                                               no    no don't                                                                              don't                                               0;a      care          care                                                                               care                  EXCEPTION, a                                                                             5382222                                                                             feature                                                                              FAC  7   yes;del all;                                                                            200  yes   dial                                                                              yes no                                                  none;c   (LWC)      tone                         EXCEPTION, a                                                                             5382333                                                                             feature                                                                              FAC  7   yes;del all;                                                                            210  yes   dial                                                                              yes no                                                  none;c   (ACB)      tone                         SYNTAX, a 5382150                                                                             fature                                                                               FAC  7   no       250  no    no yes no                                                           (TLR)                                   SYNTAX, c  654321                                                                             route account                                                                             6   no       don't                                                                               no    no don't                                                                              don't                                      code              care       care                                                                              care                      SYNTAX, c 5553689                                                                             route address                                                                             7   no       don't                                                                               no    no don't                                                                              don't                                                        care          care                                                                               care                  __________________________________________________________________________

In this implementation, the grammar matrices 400 and 410 for numbering plan "a" are illustratively populated as shown and described for FIGS. 7 and 8, while the grammar matrixes 400 and 410 for numbering plan "b" are illustratively populated as shown and described for FIGS. 23 and 24. And numbering plan "c" is a degenerative case whose grammar is irrelevant for purposes of this example.

Some aspects of the implementation merit emphasis. Despite its complexity, the above-described capability is implemented with only the few database entries listed in Table A. Also, the implementation of Table A shows two alternative ways of aliasing a network number to a feature access code. One way is to define both the network number and the feature access code substantially identically, i.e., as features having the same VNI. This is shown for the LWC and ACB features. The other way is to translate the network number into the feature access code, through restart analysis entry 333 of the network number's leaf 312. This is shown for the OP feature. The implementation can thus be seen to be very versatile, yet compact from both a design and a memory-use standpoint. Yet the implementation may be made very secure, through use of the security access code or caller I.D. scheme. The implementation places no restrictions on the kinds of symbol sequences that may be used as feature access codes in the internal dialing plan or their aliases in the external numbering plan. Extension-number portions of feature access code alias numbers may be reused for other purposes in the internal dialing plan (e.g., "2111" and "2222"). And the implementation properly handles the emergency-services access number "911" irrespective of whether it is properly dialed from switching system 10 as an external number (i.e., "9-911") or whether it is "misdialed" as an internal number (i.e., "911").

Of course, it should be understood that various changes and modifications to the illustrative embodiment described above will be apparent to those skilled in the art. For example, additional parameters can be included in the GRS matrices which cause the VNI to be converted into a routing pattern number. Or, additional parameters can be included in the GRS routing pattern tables and be associated with preferences to aid in the final preference selection. Also, additional string types and grammar rules for string type relationships can be defined. Additionally, a plurality of permissible string lengths may be defined for a given string type, and the use of alphanumeric and other characters within strings may be allowed in addition to digits. Furthermore, exception trees' contents may be incorporated into the main network syntax trees. Further still, the feature module that is invoked by the network access need not be the same module as that invoked by the corresponding FAC, but need only implement corresponding, a similar, feature. Such changes and modifications can be made without departing from the spirit and the scope of the invention and without diminishing its attendant advantages. It is therefore intended that all such changes and modifications be covered by the following claims. 

We claim:
 1. A method of invoking a feature in a switching system having an internal numbering plan in a telecommunications network having a network numbering plan, comprising the steps of:receiving at the switching system a first symbol sequence that is included in the internal numbering plan; in response to receiving the first symbol sequence, interpreting the received first symbol sequence at the switching system to be a feature access code of a feature of the switching system; receiving at the switching system a second call-control symbol sequence, different from the first symbol sequence, that is included in the network numbering plan and that is assigned, within the network numbering plan, to an extension of the switching system; in response to receiving the second symbol sequence, interpreting the received second symbol sequence at the switching system to be an equivalent of said feature access code of said feature of the switching system; and in response to the interpreting of either one of the received first symbol sequence and the received second symbol sequence, invoking said feature in the switching system.
 2. The method of claim 1 wherein:the step of interpreting the received second symbol sequence includes the step oftranslating the received second symbol sequence into the feature access code of the feature.
 3. The method of claim 1 wherein:the step of interpreting the received second symbol sequence includes the step offinding among stored definitions of symbol sequences of the network numbering plan a definition of the received second symbol sequence, which definition duplicates a stored definition of the feature access code of the feature in the internal numbering plan of the switching system.
 4. The method of claim 1 wherein:the step of interpreting the received second symbol sequence includes the step ofidentifying a pointer to a feature module, which pointer corresponds to the received second symbol sequence; and the step of invoking includes the step ofinvoking the feature module that is pointed to by the identified pointer.
 5. The method of claim 4 wherein:the step of identifying a pointer comprises the step ofidentifying the pointer, which pointer corresponds both to the received second symbol sequence and to the feature access code of the feature.
 6. The method of claim 1 wherein:the step of receiving the second symbol sequence comprises the step ofreceiving the second symbol sequence from within the network outside of the switching system.
 7. The method of claim 1 wherein:the step of receiving the second symbol sequence comprises the step ofreceiving the second symbol sequence from a user directly served by the switching system.
 8. The method of claim 1 wherein:the network is a telephony network, and the received second symbol sequence is a telephone number made up of the extension number preceded by an office code of the switching system within the telephony network.
 9. A method of invoking a feature in a switching system having an internal numbering plan in a telecommunications network having a network numbering plan, comprising the steps of:receiving at the switching system a first symbol sequence included in the network numbering plan and including an extension number of the switching system; in response to the receipt of the first symbol sequence, parsing the received first symbol sequence by using stored first information defining a syntax and a grammar of the network numbering plan and defining the first symbol sequence as a feature access code for a feature of the switching system, to determine a meaning of the first symbol sequence within the network numbering plan; and in response to the determined meaning of the received first symbol sequence, invoking said feature in the switching system.
 10. The method of claim 9 further comprising the steps ofreceiving at the switching system, from a user directly served by the switching system, a second symbol sequence included in the internal numbering plan, and in response to the receipt of the second symbol sequence, parsing the received second symbol sequence by using stored second information defining a syntax and a grammar of the internal numbering plan and defining the second symbol sequence as a feature access code for a corresponding feature, to determine a meaning of the second symbol sequence within the internal numbering plan; wherein the stored first information defines the first symbol sequence as an equivalent of the second symbol sequence, and the step of invoking comprises the step ofin response to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence, invoking the feature that corresponds to the second symbol sequence.
 11. The method of claim 10 wherein:the stored first information defines the first symbol sequence same as the stored second information defines the second symbol sequence; and the step of invoking comprises the steps ofin response to the determined meaning of the received second symbol sequence, invoking the feature that corresponds to the second symbol sequence by using the determined meaning and the stored second information, and in response to the determined meaning of the received first symbol sequence, invoking same said feature by using the determined meaning and the stored first information.
 12. The method of claim 10 wherein:the stored first information defines the first symbol sequence as translating into the second symbol sequence; the step of parsing the first symbol sequence comprises the steps ofin response to the determined meaning of the first symbol sequence, translating the first symbol sequence into the second symbol sequence, and in response to the translation, parsing the second symbol sequence resulting from the translation by using the stored second information to determine the meaning of the second symbol sequence within the internal numbering plan; and the step of invoking comprises the step ofin response to the determined meaning of either one of the received second symbol sequence and the second symbol sequence resulting from the translation, invoking the feature that corresponds to the second symbol sequence by using the determined meaning and the stored second information.
 13. A method of invoking a feature in a switching system having an internal numbering plan in a telecommunications network having a network numbering plan, comprising the steps of:receiving at the switching system, from a user directly served by the switching system, a first symbol sequence that is included in the internal numbering plan; in response to receiving the first symbol sequence, interpreting the received first symbol sequence at the switching system to be a feature access code of a feature of the switching system; in response to the interpreting of the first symbol sequence, invoking in the switching system said feature; receiving at the switching system a second call-control symbol sequence that is included in the network numbering plan and that is assigned, within the network numbering plan, to the switching system; in response to receiving the second symbol sequence, interpreting the received second symbol sequence at the switching system to be an equivalent of said feature access code of the internal numbering plan of the switching system, said feature access code being a different symbol sequence from the received second symbol sequence; and in response to the interpreting of the second symbol sequence, invoking in the switching system a like feature as is invoked by receipt of said feature access code from the user directly served by the switching system.
 14. The method of claim 13 wherein:the step of interpreting the second symbol sequence includes the step oftranslating the received second symbol sequence into the feature access code.
 15. The method of claim 13 wherein:the step of interpreting the second symbol sequence includes the step offinding among stored definitions of symbol sequences of the network numbering plan a definition of the received second symbol sequence, which definition duplicates a stored definition of the feature access code in the internal numbering plan.
 16. The method of claim 13 wherein:the step of interpreting the second symbol sequence includes the step ofidentifying a pointer to a feature module, which pointer corresponds both to the received second symbol sequence and to the feature access code; and each step of invoking includes the step ofinvoking the feature module that is pointed to by the identified pointer.
 17. The method of claim 13 wherein:the step of receiving the second symbol sequence comprises the step ofreceiving the second symbol sequence from within the network outside of the switching system.
 18. The method of claim 13 wherein:the step of receiving the second symbol sequence comprises the step ofreceiving the second symbol sequence from a user directly served by the switching system.
 19. The method of claim 18 wherein:the received second symbol sequence is an emergency-services access-number.
 20. The method of claim 13 wherein:the received second symbol sequence is a network address of the switching system within the network numbering plan.
 21. The method of claim 13 wherein:the network is a telephony network, and the received second symbol sequence is a telephone number made up of an extension number preceded by an office code of the switching system within the telephony network.
 22. A method of invoking a feature in a switching system having an internal numbering plan in a telecommunications network having a network numbering plan, comprising the steps of:receiving at the switching system, from a user directly served by the switching system, a first symbol sequence included in the internal numbering plan; in response to the receipt of the first symbol sequence, parsing the received first symbol sequence by using stored first information defining a syntax and a grammar of the internal numbering plan and defining the first symbol sequence as a feature access code for a corresponding feature, to determine a meaning of the first symbol sequence within the internal numbering plan; receiving at the switching system a second symbol sequence included in the network numbering plan; in response to the receipt of the second symbol sequence, parsing the received second symbol sequence by using stored second information defining a syntax and a grammar of the network numbering plan and defining the second symbol sequence as an equivalent of the first symbol sequence, to determine a meaning of the second symbol sequence within the network numbering plan; and in response to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence, invoking the feature that corresponds to the first symbol sequence.
 23. The method of claim 22 wherein:the stored second information defines the second symbol sequence same as the stored first information defines the first symbol sequence; and the step of invoking comprises the steps ofin response to the determined meaning of the received first symbol sequence, invoking the feature that corresponds to the first symbol sequence by using the determined meaning and the stored first information, and in response to the determined meaning of the received second symbol sequence, invoking same said feature by using the determined meaning and the stored second information.
 24. The method of claim 22 wherein:the stored second information defines the second symbol sequence as translating into the first symbol sequence; the step of parsing the second symbol sequence comprises the steps ofin response to the determined meaning of the second symbol sequence, translating the second symbol sequence into the first symbol sequence, and in response to the translation, parsing the first symbol sequence resulting from the translation by using the stored first information to determine the meaning of the first symbol sequence within the internal numbering plan; and the step of invoking comprises the step ofin response to the determined meaning of either one of the received first symbol sequence and the first symbol sequence resulting from the translation, invoking the feature that corresponds to the first symbol sequence by using the determined meaning and the stored first information.
 25. A switching system having an internal numbering plan for use in a telecommunications network having a network numbering plan, comprising:means, responsive to receipt of a first symbol sequence that is included in the internal numbering plan, for interpreting the received first symbol sequence at the switching system to be a feature access code of a feature of the switching system, and further responsive to receipt of a second call-control symbol sequence, different from the first symbol sequence, that is included in the network numbering plan and that is assigned, within the network numbering plan, to an extension of the switching system, for interpreting the received second symbol sequence to be an equivalent of said feature access code of said feature of the switching system; and means responsive to the interpretation of either one of the first symbol sequence and the second symbol sequence, for invoking said feature in the switching system.
 26. The switching system of claim 25 wherein:the interpreting means comprisemeans for translating the received second symbol sequence into the feature access code of the feature.
 27. The switching system of claim 25 wherein:the interpreting means comprisemeans for storing definitions of symbol sequences, including (a) a definition of the feature access code of the feature in the internal numbering plan of the switching system and (b) a definition of the received second symbol sequence in the network numbering plan which definition duplicates the definition of the feature access code; and means responsive to the receipt of the second symbol sequence, for finding the definition of the received second symbol sequence among the stored definitions.
 28. The switching system of claim 25 wherein:the interpreting means comprisemeans for identifying a pointer to a feature module, which pointer corresponds to the received second symbol sequence; and the invoking means comprisea plurality of feature modules including the feature module, each for implementing a feature, and means for invoking the feature module that is pointed to by the pointer identified by the pointer-identifying means.
 29. The switching system of claim 28 whereinthe identifying means comprisemeans for identifying the pointer, which pointer corresponds both to the received second symbol sequence and to the feature access code.
 30. The switching system of claim 25 wherein:the interpreting means includemeans for receiving the second symbol sequence from within the network outside of the switching system.
 31. The switching system of claim 25 wherein:the interpreting means includemeans for receiving the symbol sequence from a user directly served by the switching system.
 32. The switching system of claim 25 for use in a telephony network, wherein:the received second symbol sequence is a telephone number made up of the extension number preceded by an office code of the switching system within the telephony network.
 33. In a switching system having an internal numbering plan, for use in a telecommunications network having a network numbering plan, the improvement comprising:data storage means for storing first contents defining a syntax and a grammar of the network numbering plan that includes a first symbol sequence which first symbol sequence includes an extension number of the switching system, the first contents defining the first symbol sequence as a feature access code for a feature of the switching system; means responsive to receipt of the first symbol sequence, for parsing the received first symbol sequence by using the first contents of the data storage means to determine a meaning of the first symbol sequence within the network numbering plan; and means responsive to the determined meaning of the received first symbol sequence for invoking said feature in the switching system.
 34. The improvement of claim 33 whereinthe data storage means are further for storing second contents defining a syntax and a grammar of the internal numbering plan that includes a second symbol sequence, the second contents defining the second symbol sequence as a feature access code for a corresponding feature; the stored first information defines the first symbol sequence as an equivalent of the second symbol sequence; the parsing means are further responsive to receipt from a user directly served by the switching system of the second symbol sequence, for parsing the received second symbol sequence by using the second contents of the data storage means to determine a meaning of the second symbol sequence within the internal numbering plan; and the invoking means are responsive to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence for invoking said feature that corresponds to the second symbol sequence.
 35. The improvement of claim 33 wherein:the first contents define the first symbol sequence same as the second contents define the second symbol sequence; and the invoking means are responsive to the determined meaning of the received second symbol sequence by invoking the feature that corresponds to the second symbol sequence by using the determined meaning and the second contents of the data storage means, and are responsive to the determined meaning of the received first symbol sequence by invoking same said feature by using the determined meaning and the first contents of the data storage means.
 36. The improvement of claim 33 wherein:the first contents define the first symbol sequence as translating into the second symbol sequence; the parsing means includemeans responsive to the determined meaning of the first symbol sequence, for translating the first symbol sequence into the second symbol sequence, and means responsive to the translation, for parsing the second symbol sequence resulting from the translation by using the second contents of the data storage means to determine the meaning of the second symbol sequence within the internal numbering plan; and the invoking means are responsive to the determined meaning of either one of the received second symbol sequence and the second symbol sequence resulting from the translation, for invoking the feature that corresponds to the second symbol sequence by using the determined meaning and the second contents of the data storage means.
 37. A switching system having an internal numbering plan for use in a telecommunications network having a network numbering plan, comprising:means, responsive to receipt, from a user directly served by the switching system, of a first symbol sequence that is included in the internal numbering plan, for interpreting the received first symbol sequence at the switching system to be a feature access code of a feature of the switching system, and further responsive to receipt of a second call-control symbol sequence that is included in the network numbering plan and that is assigned, within the network numbering plan, to the switching system, for interpreting the received second symbol sequence to be an equivalent of said feature access code of the internal numbering plan of the switching system, said feature access code being a different symbol sequence from the received second symbol sequence; and means responsive to the interpretation of the first symbol sequence, for invoking in the switching system said feature, and further responsive to the interpretation of the second symbol sequence, for invoking in the switching system a same feature as is invoked by receipt of said feature access code from the user directly served by the switching system.
 38. The switching system of claim 37 wherein:the interpreting means comprisemeans responsive to receipt from a user directly served by the switching system of the second call-control symbol sequence, for interpreting the received second symbol sequence to be the equivalent of the feature access code corresponding to the feature; and the invoking means comprisemeans responsive to the interpretation of the second symbol sequence, for invoking the feature in the switching system.
 39. The switching system of claim 37 wherein:the interpreting means comprisemeans for translating the received second symbol sequence into the feature access code.
 40. The switching system of claim 37 wherein:the interpreting means comprisemeans for storing definitions of symbol sequences, including (a) a definition of the feature access code in the internal numbering plan and (b) a definition of the received second symbol sequence in the network numbering plan which definition duplicates the definition of the feature access code in the internal numbering plan; and means responsive to the receipt of the second symbol sequence, for finding the definition of the received second symbol sequence among the stored definitions.
 41. The switching system of claim 37 wherein:the interpreting means comprisemeans for identifying a pointer to a feature module, which pointer corresponds both to the received second symbol sequence and to the feature access code; and the invoking means comprisea plurality of feature modules including the feature module, each for implementing a feature, and means for invoking the feature module that is pointed to by the pointer identified by the pointer-identifying means.
 42. The switching system of claim 37 wherein:the interpreting means includemeans for receiving the second symbol sequence from within the network outside of the switching system.
 43. The switching system of claim 37 wherein:the interpreting means includemeans for receiving the second symbol sequence from a user directly served by the switching system.
 44. The switching system of claim 43 wherein:the received second symbol sequence is an emergency-services access-number.
 45. The switching system of claim 37 wherein:the received second symbol sequence is a network address of the switching system within the network numbering plan.
 46. The switching system of claim 37 for use in a telephony network, wherein:the received second symbol sequence is a telephone number made up of an extension number preceded by an office code of the switching system within the telephony network.
 47. In a switching system having an internal numbering plan, for use in a telecommunications network having a network numbering plan, the improvement comprising:data storage means for storing (a) first contents defining a syntax and a grammar of the internal numbering plan that includes a first symbol sequence, the first contents defining the first symbol sequence as a feature access code for a corresponding feature, and (b) second contents defining a syntax and a grammar of the network numbering plan that includes a second symbol sequence, the second contents defining the second symbol sequence as an equivalent of the first symbol sequence; means, responsive to receipt from a user directly served by the switching system of the first symbol sequence, for parsing the received first symbol sequence by using the first contents of the data storage means to determine a meaning of the first symbol sequence within the internal numbering plan, and further responsive to receipt of the second symbol sequence, for parsing the received second symbol sequence by using the second contents of the dam storage means to determine a meaning of the second symbol sequence within the network numbering plan; and means responsive to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence for invoking the feature that corresponds to the first symbol sequence.
 48. The improvement of claim 47 wherein:the second contents define the second symbol sequence same as the first contents define the first symbol sequence; and the invoking means are responsive to the determined meaning of the received first symbol sequence by invoking the feature that corresponds to the first symbol sequence by using the determined meaning and the first contents of the data storage means, and are responsive to the determined meaning of the received second symbol sequence by invoking same said feature by using the determined meaning and the second contents of the data storage means.
 49. The improvement of claim 47 wherein:the second contents define the second symbol sequence as translating into the first symbol sequence; the parsing means includemeans responsive to the determined meaning of the second symbol sequence, for translating the second symbol sequence into the first symbol sequence, and means responsive to the translation, for parsing the first symbol sequence resulting from the translation by using the first contents of the data storage means to determine the meaning of the first symbol sequence within the internal numbering plan; and the invoking means are responsive to the determined meaning of either one of the received first symbol sequence and the first symbol sequence resulting from the translation, for invoking the feature that corresponds to the first symbol sequence by using the determined meaning and the first contents of the data storage means.
 50. A method of invoking a feature in a switching system having an internal numbering plan in a telecommunications network having a network numbering plan, comprising the steps of:receiving at the switching system a first symbol sequence included in the internal numbering plan; in response to receiving the first symbol sequence, parsing the received first symbol sequence by using stored first information defining the internal numbering plan and defining the first symbol sequence as a feature access code for a feature of the switching system, to determine a meaning of the first symbol sequence within the internal numbering plan; receiving at the switching system a second symbol sequence, different from the first symbol sequence, that is included in the network numbering plan and including an extension number of the switching system; in response to the receipt of the second symbol sequence, parsing the received second symbol sequence by using stored second information defining the network numbering plan and defining the second symbol sequence as a feature access code for said feature of the switching system, to determine a meaning of the second symbol sequence within the network numbering plan; and in response to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence, invoking said feature in the switching system.
 51. The method of claim 50 whereinthe step of receiving a first symbol sequence comprises the step ofreceiving the first symbol sequence at the switching system from a user directly served by the switching system; and the stored second information defines the second symbol sequence as an equivalent of the first symbol sequence.
 52. The method of claim 50 wherein:the stored first information defines the first symbol sequence same as the stored second information defines the second symbol sequence; and the step of invoking comprises the steps ofin response to the determined meaning of the received second symbol sequence, invoking the feature that corresponds to the second symbol sequence by using the determined meaning and the stored second information, and in response to the determined meaning of the received first symbol sequence, invoking same said feature by using the determined meaning and the stored first information.
 53. The method of claim 50 wherein:the stored second information defines the second symbol sequence as translating into the first symbol sequence; the step of parsing the second symbol sequence comprises the steps ofin response to the determined meaning of the second symbol sequence, translating the second symbol sequence into the first symbol sequence, and in response to the translation, parsing the first symbol sequence resulting from the translation by using the stored first information to determine the meaning of the first symbol sequence within the internal numbering plan; and the step of invoking comprises the step ofin response to the determined meaning of either one of the received first symbol sequence and the first symbol sequence resulting from the translation, invoking the feature that corresponds to the first symbol sequence by using the determined meaning and the stored first information.
 54. In a switching system having an internal numbering plan, for use in a telecommunications network having a network numbering plan, the improvement comprising:data storage means for storing first contents defining the internal numbering plan that includes a first symbol sequence and defining the first symbol sequence as a feature access code for a feature of the switching system, and further for storing second contents defining the network numbering plan that includes a second symbol sequence different from the first symbol sequence, which second symbol sequence includes an extension number of the switching system, the second contents defining the second symbol sequence as a feature access code for said feature of the switching system; means responsive to receipt of the first symbol sequence, for parsing the received first symbol sequence by using the first contents of the data storage means to determine a meaning of the first symbol sequence within the internal numbering plan, and further responsive to receipt of the second symbol sequence, for parsing the received second symbol sequence by using the second contents of the data storage means to determine a meaning of the second symbol sequence within the network numbering plan; and means responsive to the determined meaning of either one of the received first symbol sequence and the received second symbol sequence, for invoking said feature in the switching system.
 55. The improvement of claim 54 whereinthe stored second information defines the second symbol sequence as an equivalent of the first symbol sequence; and the first symbol sequence is received from a user directly served by the switching system.
 56. The improvement of claim 54 wherein:the first contents define the first symbol sequence same as the second contents define the second symbol sequence; and the invoking means are responsive to the determined meaning of the received second symbol sequence by invoking the feature that corresponds to the second symbol sequence by using the determined meaning and the second contents of the data storage means, and are responsive to the determined meaning of the received first symbol sequence by invoking same said feature by using the determined meaning and the first contents of the data storage means.
 57. The improvement of claim 54 wherein:the second contents define the second symbol sequence as translating into the first symbol sequence; the parsing means includemeans responsive to the determined meaning of the second symbol sequence, for translating the second symbol sequence into the first symbol sequence, and means responsive to the translation, for parsing the first symbol sequence resulting from the translation by using the first contents of the data storage means to determine the meaning of the first symbol sequence within the internal numbering plan; and the invoking means are responsive to the determined meaning of either one of the received first symbol sequence and the first symbol sequence resulting from the translation, for invoking the feature that corresponds to the first symbol sequence by using the determined meaning and the first contents of the data storage means. 